1. Technical Field
The present disclosure relates to a plasma treatment method and a method of manufacturing an electronic component, and particularly relates to a plasma treatment method using a plasma treatment device including a cover over a stage.
Further, the present disclosure relates to a plasma treatment method and a method of manufacturing an electronic component, and particularly relates to improvement of productivity in a case where an electronic component is manufactured by performing a plasma treatment on a substrate held by a resin sheet.
2. Description of the Related Art
As a method of dicing a substrate, a plasma dicing method in which a substrate on which a resist mask is formed is subjected to plasma etching and divided into individual chips is known. Japanese Patent Unexamined Publication No. 2009-94436 and PCT Japanese Translation Patent Publication No. 2014-513868 disclose that a substrate is held by a substrate carrier including a ring-like frame and a resin sheet which covers an opening portion of the frame in order to improve handleability of the substrate during conveyance or the like. The substrate is placed on a stage in a state of being held by the substrate carrier and is subjected to a plasma treatment.
In this case, when the substrate carrier is directly exposed to plasma, a holding sheet formed of a resin material and an adhesive used to fix the holding sheet to the frame are heated. There is a concern that the substrate carrier is damaged, for example, the heating leads to elongation (deformation) of the holding sheet or degradation of adhesiveness of the adhesive and thus the holding sheet is peeled off from the frame.
Therefore, in Japanese Patent Unexamined Publication No. 2009-94436, a dielectric cover having a window portion is disposed over a stage in the inside of a reaction chamber of a plasma treatment device. The cover includes a main body portion used to cover the frame and a window portion formed to pass through the main body portion in the thickness direction. During the plasma treatment, the main body portion covers the frame and the holding sheet so that these are not exposed to plasma, and the substrate is exposed by the window portion. A portion, on which a resist mask is not formed, in the exposed substrate is etched by plasma.
The resin sheet is adsorbed by the stage typically due to an electrostatic adsorption mechanism referred to as an electrostatic chuck. The electrostatic adsorption mechanism includes an electrode for electrostatic adsorption (electrostatic chunk) (hereinafter, referred to as an ESC electrode) disposed in the inside of the stage. When a voltage is applied to the ESC electrode, Coulomb force is generated in a space between the ESC electrode and the substrate carrier and Johnsen-Rahbek force is generated in a space between the stage and the substrate carrier. The electrostatic adsorption mechanism allows the stage to adsorb the resin sheet using the above-described electrostatic force.
In a plasma treatment process, in order to perform vertical etching on the surface of a substrate, an etching step using plasma of fluorine-based gas such as SF6 and a protective film deposition step using plasma of fluorocarbon gas such as perfluorocyclobutane (CFO are alternately repeated in some cases.
When the plasma treatment is continuously performed on a plurality of substrates using such a method, adhesive materials are accumulated in the reaction chamber as the number of treated substrates is increased, and thus the substrates are contaminated or desired etching cannot be carried out in some cases.
An adhesive material is, for example, a substance containing carbon and is adhered to a surface (hereinafter, referred to as a rear surface of the cover) facing a stage of a cover. The substance is a reaction product derived from fluorocarbon gas used in the above-described protective film deposition step. During the plasma treatment, since the cover protects a frame and a holding sheet from plasma, the cover is disposed in a position which is not in contact with the frame and the holding sheet and is as close to the frame and the holding sheet as possible.
In the protective film deposition step, the fluorocarbon gas introduced to the reaction chamber is decomposed to ions or radicals in the plasma, and some of these enter a space between the cover and the stage and are brought into contact with the rear surface of the cover. In this manner, a reaction product containing carbon derived from the fluorocarbon gas is adhered to the rear surface of the cover.
In the etching step, the fluorine-based gas introduced to the reaction chamber is decomposed to ions or radicals in the plasma, and some of these enter the space between the cover and the stage in the same manner as described above. In the etching step, a bias voltage is typically applied to the stage. In this manner, the speed at the time of a decomposition component of the fluorine-based gas colliding with the substrate placed on the stage is increased and thus the etching reaction is promoted. However, since the rear surface of the cover is positioned over the stage in a state of being separated from the stage, the effect for promoting the etching reaction with respect to the rear surface of the cover is unlikely to be obtained even when a bias voltage is applied to the stage. Therefore, the decomposition component of the fluorine-based gas having entered the space between the cover and the stage is unable to sufficiently remove the reaction product adhered to the rear surface of the cover in the protective film deposition step. As a result, the reaction product is accumulated on the rear surface of the cover whenever the plasma treatment process is repeated. The accumulated reaction product is eventually peeled off from the rear surface of the cover and then falls onto the stage or the substrate or is suspended in the reaction chamber. Therefore, the substrate is contaminated or desired etching cannot be carried out.
In a case where the plasma treatment is continuously performed on a plurality of substrates respectively held by a resin sheet, there is a tendency that the depth (etching rate) obtained from the etching within a predetermined time is decreased as the number of treated substrates is increased. Further, an adhesive matter is generated on the stage after the plasma treatment is performed on the substrates respectively held by a resin sheet such that the shape of a resin sheet is transferred. It is understood that a decrease in etching rate is affected by the adhesive matter.
During the plasma treatment, heat generated by irradiation with plasma or an electric field and a leakage current generated by the ESC electrode are added to the resin sheet. Accordingly, it is considered that various additives such as a plasticizer contained in the resin sheet are discharged from the resin sheet, suspended on the surface of the resin sheet, and adhered to the stage during the plasma treatment. A large amount of adhesive matter, resulting from the resin sheet, is generated particularly from a portion of the resin sheet holding the substrate. As described above, a phenomenon in which various additives contained in the resin are suspended on the surface of the resin is referred to as bleed-out.
Here, the stage is typically cooled (for example, 15° C. or lower) in order to suppress thermal damage to the resin sheet by being heated through irradiation with plasma. When the stage is cooled, the resin sheet in close contact with the stage is also cooled by electrostatic adsorption. However, when an adhesive matter is interposed between the resin sheet and the stage, the effect for cooling the resin sheet is decreased. When the resin sheet is not sufficiently cooled, the effect for cooling the substrate held by the resin sheet is also decreased. Therefore, the etching rate is reduced and then the productivity is decreased. In a case where a substrate is continuously treated, since it is necessary to stop a process for removal of an adhesive matter of the stage, the productivity is further decreased.